PHOTOAQUATION OF CIS-DICHLOROBIS(1,10-PHENANTHROLINE)CHROMIUM(III) AND THE PHOTOCHEMICAL AND THERMAL-REACTIONS OF THIS COMPLEX WITH NATIVE CALF-THYMUS DNA

The photoaquation of the title compound [cis-Cr(phen)(2)Cl-2(+)] has b een studied using high performance liquid chromatography. Both monoaqu o [cis-Cr(phen)(2)Cl(OH2)(2)(2+)] and diaquo [cis-Cr(phen)(2)(OH2)(2)( 3+)] products are formed, and the quantum efficiency for the loss of s tarting material in Tris buffer (pH 7) under argon and oxygen is 0.010 +/- 0.001 and 0.0026 +/- 0.0002, respectively. The presence of deoxyg uanosine (dG) increases the rate of loss, as much as twofold under arg on, but only the rate of diaquo product formation is enhanced by the n ucleoside. The dG effect is attributed to reductive quenching of the c is-Cr(phen)(2)Cl-2(+) excited state by the base. Equilibrium dialysis studies indicate that both cis-Cr(phen)(2)Cl-2(+) and cisCr(phen)(2)(O H2)(2)(3+) minimally associate with calf-thymus DNA. However, photolys es of cis-Cr(phen)(2)Cl-2(+) with the nucleic acid yield a mixture of unidentified covalent adducts. The diaquo complex also forms covalent adducts with DNA in the absence of light. Photolyses of the cis-Cr(phe n)(2)Cl-2(+) with polyribonucleotides indicate a clear preference for covalent binding to the purines.